Fluorescence Quantum Yield and Single-Particle Emission of CdSe Dot/CdS Rod Nanocrystals
Fluorescence Quantum Yield and Single-Particle Emission of CdSe Dot/CdS Rod Nanocrystals
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DOI：
10.1021/acs.jpcc.9b07957
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发表时间：
2019-10-03
影响因子：
3.7
通讯作者：
Mews, Alf
中科院分区：
文献类型：
--
作者：
Hinsch, Alexandra;Lohmann, Sven-Hendrik;Mews, Alf
CdSe dot/CdS rod（DR）纳米粒子系综的荧光量子产率（QY）依赖于壳层生长和激发波长。我们分析了这种依赖性的起源，通过比较DR合奏的光学性质，在单粒子实验中获得的结果。在系综水平上，我们发现，与壳层长度小于40 nm的DR的QY表现出不依赖于激发波长，而与壳层长度大于50 nm的DR，QY显着降低激发CdS带隙以上。在激发的CdSe核心，系综QY，荧光波长，和荧光闪烁行为的个别颗粒仅取决于径向CdS壳层厚度，而不是CdS壳层长度。如果光生激子可以到达CdSe核心区域，则荧光性质将仅取决于靠近CdSe核心的表面钝化。量子产率的变化时，激发以上的CdS的带隙较长的DR不能被解释为非辐射粒子，因为发射DR的比率被发现是独立的DR长度。我们提出了一个模型，在QY较长的CdS壳减少后，是由于在拉长的壳内的非辐射激子复合的比例增加。这得到基于有效质量近似的计算的支持，该计算表明DR的最佳长度为约40 nm，以将高CdS吸收截面的益处与高荧光QY联合收割机结合。
The fluorescence quantum yield (QY) of CdSe dot/CdS rod (DR) nanoparticle ensembles is dependent on the shell growth and excitation wavelength. We analyze the origin of this dependency by comparing the optical properties of DR ensembles to the results obtained in single-particle experiments. On the ensemble level, we find that the QY of DRs with shell lengths shorter than 40 nm exhibits no dependence on the excitation wavelength, whereas for DRs with shell lengths longer than 50 nm, the QY significantly decreases for excitation above the CdS band gap. Upon excitation in the CdSe core, the ensemble QY, the fluorescence wavelength, and the fluorescence blinking behavior of individual particles are only dependent on the radial CdS shell thickness and not on the CdS shell length. If the photogenerated excitons can reach the CdSe core region, the fluorescence properties will be dependent only on the surface passivation in close vicinity to the CdSe core. The change in QY upon excitation above the band gap of CdS for longer DRs cannot be explained by nonradiative particles because the ratio of emitting DRs is found to be independent of the DR length. We propose a model after which the decrease in QY for longer CdS shells is due to an increasing fraction of nonradiative exciton recombination within the elongated shell. This is supported by an effective-mass-approximation-based calculation, which suggests an optimum length of DRs of about 40 nm, to combine the benefit of high CdS absorption cross section with a high fluorescence QY.